A dispersion is a system in which one or more dispersed phases are distributed throughout a dispersion medium. The dispersed phase and the dispersion medium may both be comprised of one or more solids, liquids, gases or supercritical fluids.
The study of dispersions is relevant to many fields and industries. Generally speaking, such study is often performed in order to obtain information relating to the character or nature of a particular dispersion system under selected or defined conditions.
The information obtained from such study may be used for many purposes, including for the optimization or enhancement of the composition of a particular dispersion for use under defined conditions or for the optimization or enhancement of the conditions to which a particular dispersion may be exposed in order to achieve a desired result or effect. In other words, the information may be used to tailor either or both of the composition of the dispersion or the conditions to which the dispersion may be exposed in order to achieve the desired result or effect.
The study of a dispersion often involves analysis or characterization relating to the interaction amongst the constituents of the dispersion. This interaction is influenced by the behaviour of the interfaces between the constituents, which behaviour is defined by the interfacial properties of the dispersion. The interfacial properties of a dispersion may be dependent upon time, upon the composition of the dispersion, and upon the conditions, such as pressure and temperature, to which the dispersion is subjected.
Interfacial properties may affect the stability of a dispersion as well as the relative solubility and/or miscibility of the constituents of the dispersion.
As one example, the stability of a foam or an emulsion may be governed by the interfacial properties of the constituents of the foam or emulsion. As a second example, the tendency of solid particles in a dispersion to undergo precipitation, flocculation, agglomeration or deposition may be governed by the behaviour of the solid particles relative to the dispersion medium. As a third example, the ability of a first fluid in a dispersion to mix with a second fluid in the dispersion may be governed by the interfacial properties of the first fluid and the second fluid.
Interfacial properties are important in enhanced oil recovery processes which involve fluid/gas flooding of oil reservoirs. In such processes, the goal is often to achieve miscibility between the flooding fluid (sometimes referred to as a solvent) and the hydrocarbon liquid contained in the reservoir. Miscibility is a state in which the interfaces between constituents of a dispersion essentially disappear as the interfacial tension between the constituents approaches zero.
When miscibility is achieved, the flooding fluid or solvent and the hydrocarbon liquid essentially move as a single phase so that the hydrocarbon liquid may be effectively flushed from the reservoir by the flooding fluid.
It is therefore desirable to know in advance the conditions, such as temperature and pressure, under which a dispersion comprising hydrocarbon liquid and a flooding fluid will become miscible. Of particular interest is the “minimum miscibility pressure” of the dispersion, which is the minimum pressure at which the hydrocarbon liquid and the flooding fluid will become miscible at a given temperature.
Several methods exist in the prior art for determining the minimum miscibility pressure of a dispersion in the context of enhanced oil recovery processes.
One prior art method for determining minimum miscibility pressure is the conventional Slim Tube Test. In the Slim Tube Test, a coiled slim tube apparatus about 4 millimeters to about 19 millimeters in diameter and about 15 to 20 meters long is packed with sand and then filled with a hydrocarbon liquid of interest. A volume of a flooding fluid or solvent equal to 1.2 times the pore volume of the slim tube apparatus is then injected at a constant pressure into one end of the slim tube apparatus and the volume of hydrocarbon liquid produced at the other end of the slim tube apparatus is measured. The test is repeated at different constant pressures in order to obtain at least four data points representing the produced volume of hydrocarbon liquid as a function of pressure. The minimum miscibility pressure of the hydrocarbon liquid and the flooding fluid or solvent is then determined from the data points.
Although the conventional Slim Tube Test can provide useful results, the method does have limitations. For example, the Slim Tube Test requires relatively large sample volumes, typically requires several days in order to complete each test, and has a maximum operating pressure of only about 70 MPa.
A second prior art method is the Rising Bubble Test. In the Rising Bubble Test, a discrete bubble of a flooding fluid or solvent is injected into the lower end of a windowed pressure vessel which is maintained at a constant pressure and temperature. The rising of the bubble in the vessel is observed to determine whether the bubble dissolves or dissipates before it reaches the top of the vessel. If the bubble totally dissolves, the hydrocarbon liquid/flooding fluid dispersion is considered to be miscible at the particular temperature and pressure. If the bubble does not totally dissolve, the pressure is incrementally increased and the test is repeated until the minimum miscibility pressure at the particular temperature is determined.
The Rising Bubble Test is described in U.S. Pat. No. 4,627,273 (Christiansen et al). Variations of the Rising Bubble Test are described in U.S. Pat. No. 4,610,160 (Christiansen), U.S. Pat. No. 4,621,522 (Christiansen et al), and U.S. Pat. No. 5,505,074 (Mihcakan et al).
The Rising Bubble Test requires relatively smaller sample volumes than does the Slim Tube Test and requires significantly less time than the Slim Tube Test to perform (up to ten or fifteen tests per day may be performed using a single Rising Bubble Test apparatus). However, the Rising Bubble Test has a maximum operating pressure of only about 35 MPa. In addition, since the solvent bubble must be observed “rising” in the pressure vessel, there are limitations in the types of hydrocarbon liquids which may be evaluated using the Rising Bubble Test. For example, the hydrocarbon liquid must be relatively transparent or translucent in order to permit observation of the rising bubbles and the hydrocarbon liquid must have a relatively moderate viscosity in order to facilitate rising of the bubbles therein.
Other prior art methods and approaches for determining minimum miscibility pressure in enhanced oil recovery applications are discussed in: (1) Kechut, Nor Idah; Zain, Zahidah Md.; Ahmad, Noraini; and Ibrahim, Anwar Raja, “New Experimental Approaches in Minimum Miscibility Pressure (MMP) Determination”, SPE 40286, 1999; (2) Zain, Zahidah Md.; Kechut, Nor Idah; Nadeson, Ganesan; Ahmad, Noraini; Raja, Dr. D. M. Anwar, “Evaluation of CO2 Gas Injection for Major Oil Production Fields in Malaysia-Experimental Approach Case Study: Dulang Field”, SPE 72106, 2001; (3) U.S. Pat. No. 4,455,860 (Cullick et al); and (4) U.S. Pat. No. 4,766,558 (Luks et al).
There remains a need for an apparatus and a method for characterizing an interfacial property of a dispersion, such as minimum miscibility pressure, which addresses some or all of the limitations of the prior art apparatus and methods. There is a particular need for a method for characterizing an interfacial property of a dispersion which utilizes images and image processing techniques and for an apparatus which can be used for collecting images for processing in the method and which may also facilitate other aspects of the performance of the method.